If images of the internal structure of real specimens are not
available, then the packed states need to be generated by some type of
stochastic packing generator. There are no generators which
are known to sample from the same ensemble as a physical process. The
first generators used, based on
ballistic methods [1]}, [2]}, [3]}, [4]}
or on the rearrangements of random point patterns
[5]}, [6]}, [7]}, [8]}, [9]}, [10]},
have no basis in the physics of packing formation at all. Models
based on Discrete Element Methods [DEM]
[11]}, [12]}, [13]}, [14]} are inspired by the physics of
packing formation, but all are based on unverifiable assumptions about
how grains interact. It is possible to avoid
these issues by assuming that any packing generator which can produce
the right mean volume fraction of grains is good enough, but
this is a dangerous assumption. If the generator
produces initial arrangements of grains which possess structure not found in
physical specimens, then any model of an aspect of powder flow which depends on initial grain arrangements may be useless.
